1. Field of the Invention
This invention relates to squarylium compounds which absorb near infrared rays, and to an optical information recording medium using the same.
2. Discussion of Background
Materials which absorb near infrared rays have various uses, for instance, for (i) safe-light filters for photosensitive materials which are sensitive to infrared rays; (ii) infrared-light-cutting filters for controlling the growth of plants; (iii) materials for cutting heat rays of sunlight; (iv) infrared-light-cutting filters for protecting eye tissues from infrared rays; (v) infrared-light-cutting filters for light receiving elements of semiconductors.
In addition to the above, a recording material for use in an optical information recording medium is one of important uses of the near-infrared-rays-absorbing materials.
Hitherto, cyanine dyes such as phthalocyanine dyes; phenanthrene dyes; naphthoquinone dyes; and pyrylium dyes have been known as infrared-absorbing materials, and optical information recording media comprising such dyes have also been disclosed, for example, in Japanese Laid-open Patent Application 55-97033, 58-83344, 58-224793, 58-214162 and 59-24692.
Phthalocyanine dyes, however, are disadvantageous in that they have low photosensitivity and high decomposition temperatures, and are not readily vacuum-deposited. Further, since they have extremely low solubility in organic solvents, they cannot be coated by liquid coating.
Phenanthrene and naphthoquinone dyes are readily vacuum-deposited, but low in reflectance. The low reflectance causes a low contrast between a recorded area and a non-recorded area when recorded by laser beams. This will bring about inaccurate reproduction of recorded information.
Pyrylium and cyanine dyes are soluble in solvents, so that they can be coated by liquid coating. However, since these dyes have low light resistance, they are readily deteriorated by the light employed for the reproduction of recorded information.